Sharif Digital Repository

Diffusivity equation which can provide us with the pressure distribution, is a Partial Differential Equation (PDE) describing fluid flow in porous media. The quadratic pressure gradient term in the diffusivity equation is nearly neglected in hydrology and petroleum engineering problems such as well test analysis. When a compressible liquid is injected into a well at high pressure gradient or when the reservoir possess a small permeability value, the effect of ignoring this term increases. In such cases, neglecting this parameter can result in high errors. Previous models basically focused on numerical and semi-analytical methods for semi-infinite domain. To the best of our knowledge, no... 

The bronchial tree plays a main role in the human respiratory system because the air distribution throughout the lungs and gas exchange with blood occur in the airways whose dimensions vary from several centimeters to micrometers. Organization of about 60,000 conducting airways and 33 million respiratory airways in a limited space results in a complex structure. Due to this inherent complexity and a high number of airways, using target-oriented dimensional reduction is inevitable. In addition, there is no general reduced-order model for various types of problems. This necessitates coming up with an appropriate model from a variety of different reduced-order models to solve the desired... 

The bronchial tree plays a main role in the human respiratory system because the air distribution throughout the lungs and gas exchange with blood occur in the airways whose dimensions vary from several centimeters to micrometers. Organization of about 60,000 conducting airways and 33 million respiratory airways in a limited space results in a complex structure. Due to this inherent complexity and a high number of airways, using target-oriented dimensional reduction is inevitable. In addition, there is no general reduced-order model for various types of problems. This necessitates coming up with an appropriate model from a variety of different reduced-order models to solve the desired... 

Present investigation analyzes the issue of entropy generation in a uniformly heated microchannel heat sink (MCHS). Analytical approach used to solve forced convection problem across MCHS, is porous medium model based on modified Darcy equation for fluid flow and two-equation model for heat transfer between solid and fluid phases. Furthermore, closed form solution of velocity distribution is employed to capture z-direction velocity gradient of flow, which plays a salient role on entropy generation through fluid flow. Analytical expressions for total and thermal entropy generation number (stems from heat transfer), and Bejan number are derived and cast into dimensionless form using velocity... 

In this article, the problem of simultaneous heat, mass, and momentum transfer in the developing region of tubular reactors with homogeneous chemical reaction and laminar power-law fluid flow under unsteady-state conditions has been solved. In this regard, the general governing equations were solved using finite-difference method and analyzed carefully. Moreover, the influences of various parameters and dimensionless numbers such as power-law index, heat of reaction, reaction order, and Damköhler number value on the numerical results were investigated. In addition, the numerical results obtained for the fully-developed velocity distribution of Newtonian fluid flow and Sherwood number value... 

This study provides a stability analysis of flexible rotating pipes taking into account the simultaneous effects of internal and external fluid loading. Using the Euler-Bernoulli beam assumptions, governing equations for flexural vibrations of rotating pipes are obtained. The internal flow characteristics and the double gyroscopic effect are taken into account when deriving the structural equations coupled with the internal flow. External fluid loading is determined by a special linearization of the Navier-Stokes equations. Considering the circular wall of the pipe as an impermeable boundary to the flow, fluid-induced forcing functions are obtained and then applied to the structural... 

This study provides a stability analysis of flexible rotating pipes taking into account the simultaneous effects of internal and external fluid loading. Using the Euler-Bernoulli beam assumptions, governing equations for flexural vibrations of rotating pipes are obtained. The internal flow characteristics and the double gyroscopic effect are taken into account when deriving the structural equations coupled with the internal flow. External fluid loading is determined by a special linearization of the Navier-Stokes equations. Considering the circular wall of the pipe as an impermeable boundary to the flow, fluid-induced forcing functions are obtained and then applied to the structural... 

Natural flyers have flexible wings, which deform significantly under the combined inertial and aerodynamic forces. In this study, we focus on the role of chord wise flexibility in 2D pitch and plunge motions. We derive the exact nonlinear 2D equations of motion for a flexible flapping wing with flying support. In achieving the closed-form equations, we use the exact strain field concerning considerable elastic deformations. After numerically solving the novel equations, we validate them in simulations with highly deformable wings. By coupling the derived equations of motion with fluid flow, we study the aerodynamic performance of the geometrically nonlinear flexible flapping wing. Through... 

A new characteristic-based method is developed and used for solving the mixed and forced convection problems. The nano-fluid flow with heat transfer is simulated with a novel characteristic-based scheme in closed domains with different aspect ratios. For this purpose, a FORTRAN code has been written and developed. Water as a pure fluid and water-titanium dioxide as a nano-fluid were considered. The governing equations are solved by the finite volume utilizing a characteristic-based scheme for the convective fluxes. The simulation is done at Grashof numbers from 100 to 104, Reynolds numbers from 100 to 1000, and volume fractions of nano-particles from 0% to 10%. Streamlines, isotherms,... 

In this paper, the fluid-structure interaction problem in mechanical systems in which a high frequency vibrating solid structure interacts with the surrounding fluid flow is considered. Such a situation normally appears in many microelectromechanical systems like a wide variety of microfluidic devices. A different implementation of the residual-based variational multiscale flow method is employed within the arbitrary Lagrangian-Eulerian formulation. The combination of the variational multiscale method with appropriate stabilization parameters is used to handle the so-called small time step instability in the finite element analysis of the fluid part in the coupled fluid-structure interaction... 

The dynamics of a pressure regulator valve have been studied using the through Bondgraph simulation technique. This valve consists of several elements that can transmit, transform, store, and consume hydraulic energy. The governing equations of the system have been derived from the dynamic model. In solving system equations numerically, various pressure-flow characteristics across the regulator ports and orifices have been taken into consideration. This simulation study identifies some critical parameters that have significant effects on the transient response of the system. The results have been obtained using the MATLAB-SIMULINK environment. The main advantage of the proposed methodology... 

Density Current is formed when a fluid with heavier density than the surrounding fluid flows down an inclined bed. These types of flows are common in nature and can be produced by; salinity, temperature inhomogeneities, or suspended particles of silt and clay. Driven by the density difference between inflow and clear water in reservoirs, density current plunges clear water and moves towards a dam, while density current flows on a sloping bed. The vertical spreading due to water entrainment has an important role in determining the propagation rate in the longitudinal direction. In this work, two-dimensional steady-state salt solutions' density currents were investigated by means of... 

Among numerous methods which have been employed to reinforce the thermal efficiency in many systems, one is the thermal radiation which is a mode of heat transfer. Another way to improve the thermal efficiency is the utilization of the porous media. The present work includes the study of micropolar flow with allowance for thermal radiation through a resistive porous medium between channel walls. The governing coupled partial differential equations representing the flow model are transmuted into ordinary ones by using the suitable dimensionless coordinates, and then, quasi-linearization is employed to solve the set of relevant coupled ODEs. Effects of physical parameters on the flow under... 

Among numerous methods which have been employed to reinforce the thermal efficiency in many systems, one is the thermal radiation which is a mode of heat transfer. Another way to improve the thermal efficiency is the utilization of the porous media. The present work includes the study of micropolar flow with allowance for thermal radiation through a resistive porous medium between channel walls. The governing coupled partial differential equations representing the flow model are transmuted into ordinary ones by using the suitable dimensionless coordinates, and then, quasi-linearization is employed to solve the set of relevant coupled ODEs. Effects of physical parameters on the flow under... 

An enhancement in heat transfer due to nanofluids is essentially required in various thermal systems. Hybrid nanofluids possess high thermal conductivity and, have ability to embellish and enhance the thermal strength of common fluids. Our concern in this paper is to examine the innovative attributes of hybrid nanofluids like Manganese zinc ferrite (MnZnFe2O4) and Nickel zinc ferrite (NiZnFe2O4) in the bio-convective flow of motile gyrotactic microorganisms subject to Darcy Forchheimer medium. The effect of activation energy has also been taken into account. Mathematical treatment is carried out via MATLAB software. The use of MnZnFe2O4 - NiZnFe2O4/H2O exhibits improved thermal... 

Hybrid nanofluids are new and most fascinating types of fluids that involve superior thermal characteristics. These fluids exhibit better heat-transfer performance as equated to conventional fluids. Our concern, in this paper, is to numerically interpret the kerosene oil-based hybrid nanofluids comprising dissimilar nanoparticles like silver (Ag) and manganese zinc ferrite (MnZnFe2O4). A numerical algorithm, which is mainly based on finite difference discretization, is developed to find the numerical solution of the problem. A numerical comparison appraises the efficiency of this algorithm. The effects of physical parameters are examined via the graphical representations in either case of... 

Valveless piezoelectric micropumps are in wide practical use due to their ability to conduct particles with absence of interior moving mechanical parts. The objective of this paper is to obtain the fluid flow response to actuation frequency of a passive diffuser valve under harmonic pressures. In this regards a 2D model of a micropump valves and chambers is analyzed. The analysis is performed for 10Kpa back pressure on micropump chamber and actuation frequencies within the range of 1Hz to 10 KHz. Results show the highest velocity in the direction of diffuser axis occurs at the narrow diffuser neck while flow direction reverses every half period. For low frequencies, a parabolic velocity... 

The particle shape is an important factor playing critical role in evaluation of the interactions between particles in high-concentration particle-fluid flows. In this paper, the well-known multisphere (MS) approximation approach and the novel rolling resistance approach are utilized to examine their performance in order to simplify the generalized shaped particle’s interactions within the framework of discrete element method (DEM) and computational fluid dynamics (CFD). The performance of two approaches are compared with the perfect particle’s shape geometry, for the limited cases of cubic-shaped and disk-shaped particle flows in a horizontal well drilling process as a reference scenario.... 

During the well drilling process, particles are produced in different shapes. The shape of particles can influence the characteristics of particles transport process. The aim of this work is to analyze the effects of particle shape on the transportation mechanism. For this purpose, a three-dimensional model is prepared for simulation of particle transportation with spherical and non-spherical shapes, during deviated well drilling. The motion of particles and the non-Newtonian fluid flow are simulated via discrete element method and CFD, respectively. The two-way coupling scheme is used to incorporate the effects of fluid-particle interactions. Three different samples of non-spherical shapes... 

The particle shape is an important factor playing critical role in evaluation of the interactions between particles in high-concentration particle-fluid flows. In this paper, the well-known multisphere (MS) approximation approach and the novel rolling resistance approach are utilized to examine their performance in order to simplify the generalized shaped particle’s interactions within the framework of discrete element method (DEM) and computational fluid dynamics (CFD). The performance of two approaches are compared with the perfect particle’s shape geometry, for the limited cases of cubic-shaped and disk-shaped particle flows in a horizontal well drilling process as a reference scenario....